1. Field of the Invention
The present invention generally relates to a capacitor and, more particularly, to a capacitor containing at least two anodes that are connected to a common terminal within the capacitor casing.
2. Description of Related Art
As more and more medical applications are investigated and implemented to aid and assist the human body, devices needed to deliver the desired therapy are becoming increasingly more sophisticated, both functionally and in terms of their structural makeup. Modern implantable devices require power sources that are smaller in size, but powerful enough to meet the therapy requirements. For example, a cardiac defibrillator has a battery powering circuits performing such functions as, for example, the heart sensing and pacing functions. This requires electrical current of about 1 microampere to about 100 milliamperes. From time-to-time, the cardiac defibrillator may require a generally high rate, pulse discharge load component that occurs, for example, during charging of a capacitor assembly in the defibrillator for the purpose of delivering an electrical shock to the heart to treat tachyarrhythmias, the irregular, rapid heartbeats that can be fatal if left uncorrected. This requires electrical current of about 1 ampere to about 4 amperes.
The current trend in medicine is to make cardiac defibrillators, and like implantable devices, as small and lightweight as possible without compromising their power. This, in turn, means that capacitors contained in these devices must be readily adaptable in how they are connected to each other as well as to the battery and the device circuitry. In that light, a number of patents and publications disclose electrical energy storage devices including capacitors having a dual anode structure.
One is U.S. Pat. No. 6,850,405 to Mileham et al., which is assigned to the assignee of the present invention and incorporated herein by reference. This patent relates to a design that provides two anodes and their associated feedthroughs incorporated into one capacitor. The feedthrough wires can be in their own glass-to-metal seal or, they can be combined into one glass-to-metal seal as long as they are electrically insulated from each other. One embodiment has the two anode feedthrough wires left unconnected outside the capacitor. In another, they are joined externally of the capacitor casing. Several interconnect designs are described, none of which include a connection of the anode leads within the capacitor casing.
U.S. Pat. No. 7,012,799 to Muffoletto et al., which is also assigned to the assignee of the present invention and incorporated herein by reference, describes an enclosure for a wet tantalum electrolytic capacitor or for an electrochemical cell such as a lithium/silver vanadium oxide cell. In one embodiment, the capacitor comprises a metallic enclosure of a first drawn portion, and a second stamped cover. The enclosure houses two anodes in a side-by-side relationship. Each anode includes an embedded anode wire weld contacted to an anode lead that is electrically insulated from the casing by a glass-to-metal seal. The anode wires are not connected within the capacitor casing.
U.S. Pat. No. 6,679,926 to Kajiura et al., which is incorporated herein by reference, describes a lithium secondary battery including a cathode of a porous sintered material made of a lithium-transition metal oxide in electrochemical association with several pairs of anodes made of a sintered material joined onto a rectangular anode current collector. The anode current collector has a strip-shaped anode lead that protrudes at one end thereof. In an electrode assembly, a plurality of extending anode leads is bundled into an anode-connecting conductor, which is welded onto an anode terminal via an insulation plate.
More specifically, Kajiura et al. relates to a battery having multiple rectangular or square anodes and cathodes that are stacked in a generally alternating arrangement. In the various battery embodiments, the multiple anodes are interconnected with a strip shaped anode current collector, and the multiple cathodes are also interconnected with a strip shaped cathode current collector. The sections of anode or cathode current collector that are provided between the planar rectangles of anode or cathode are flexible. This enables stacking sequences of cathodes in a serpentine manner or rolling the cathodes in a jellyroll configuration. The anodes are interspersed therebetween in both embodiments.
At numerous instances in the Kajiura et al. patent, the importance of precisely aligning the series of anodes and cathodes in a layered sequence to achieve a battery of high capacity is emphasized. For example, at column 2, lines 28 to 46, it is disclosed that, “[w]hen an electrode unit consisting of one sintered cathode and one sintered anode is to be assembled, for example, both electrodes can be easily aligned with each other simply by stacking the cathode and the anode to oppose each other while interposing a separator therebetween. However, when a battery having an electrode unit consisting of a number of pairs of cathode and anode is to be assembled for the purpose of achieving a large battery capacity, a plurality of cathodes and anodes must be accurately aligned to oppose each other via separators. This leads to a longer period of time for stacking the electrodes and the electrode unit, or requires it to use a high precision apparatus for alignment. Also there has been such a problem that, when moving a stacking electrode unit or housing the stacking electrode unit in a battery casing after the stacking process, the electrodes are shifted from the predetermined positions, thus leading to a decrease in the area over which the mating electrodes face each other, and resulting in a decrease in the battery capacity of the completed battery.” One object of the Kajiura et al. invention is “to provide a lithium battery that comprises the electrode made of a plurality of sintered materials, where the cathodes and the anodes will not be shifted from the predetermined positions and high reliability is ensured.” Kajiura et al. repeatedly teach cathode and anode structures wherein the current collectors are rectangular strips of material. For example, with reference to FIG. 1A in this patent, at column 10, lines 32 to 48, it is disclosed that, “[t]he cathode sheet 2 comprises a strip-shaped cathode current collector 4 and a plurality of cathodes 3 made of sintered material aligned on and joined to one side of thereof. The plurality of cathodes 3 are joined while being spaced from one another at a plurality of bending portions 5 that secure spaces required for bending and are defined by desirable intervals on the cathode current collector 4. The anode sheet 6 has a structure similar to that of the cathode 2, including a strip-shaped anode current collector 8 and a plurality of anodes 7 made of sintered material aligned on and joined to one side of thereof, the plurality of anodes 7 being joined while being spaced from one another at a plurality of bending portions 10 defined by desirable intervals on the anode current collector 8. In the anode sheet 6, one end of the strip-shaped anode current collector 8 is stretched in the longitudinal direction to form the anode lead 9.”
With reference to FIG. 3D, at column 12, lines 9 to 21, it is disclosed that, “[f]or the anodes, for example, a pair of anodes 7 made of the sintered material joined onto a rectangular anode current collector 8′ may be used. The anode current collector 8′ has the strip-shaped anode lead 9 that protrudes at one end thereof. The plurality of anode leads 9 extending from the front end of the stacked electrode 15 is bundled into an anode-connecting conductor 12 (FIG. 3D). Then the anode connecting conductor 12 is welded onto the anode terminal 20 via an insulation plate 16, while the stacked electrode 15 is housed in the can 17 so that the rear end of the stacked electrode 15 and the cathode current collector on the outermost layer make contact with the bottom and the wall of the can 17 (FIG. 1E). The subsequent process to complete the battery is similar to the case of the first embodiment (FIG. 3F). An anode sheet that includes a plurality of anodes made of sintered material may be used instead of the cathode sheet, and sintered cathodes may be used instead of the sintered anodes. In the battery C, since the sintered electrode sheet is folded after covering the sintered electrodes, the electrodes can be aligned easily and displacement of the electrodes can be prevented.”
It is apparent from the teachings of Kajiura et al. that the flexible regions of the anode and cathode current collectors not only provide electrical continuity between the rectangular anode and cathode plates, but these regions also serve a critical function in achieving and maintaining alignment of the cathode and anode plates in order to provide a battery of high capacity. The flexed regions, which are typically bent 180 degrees within the battery casing, have lines of contact along the upper and lower ends of the battery casing, and the outer edges that extend beyond the lateral boundaries of the anodes and cathodes are also in contact with, or in close proximity to the lateral walls of the battery casing. This compact geometrical configuration thus constrains the anodes and the cathodes within the battery casing. It prevents any significant motion of these electrodes relative to each other, which could misalign the electrodes and reduce the battery capacity. The only instance in which a wire conductor is connected to the anodes or cathodes is at an end point of the strip shaped current collector, where a termination is needed for connection to one of the battery terminals.
It is apparent that were Kajiura et al. to use individual wire connectors between the anode and/or cathode plates in lieu of the flexible strip shaped regions, the ability to easily align the anodes and cathodes in a stacked configuration during battery fabrication, and to maintain the critical alignment during battery use would be lost. Such a battery would thus be rendered unsuitable for its intended purpose.
Additionally, Kajiura et al. provide teachings regarding preparation of the anodes and cathodes by pressing and sintering active materials, or by coating active materials on the current collectors. For each of these fabrication methods, the use of intermittent current collector strips connected by wire bridges would result in additional challenges. Sintering requires uniform heat transfer, which is problematic with a discontinuous substrate. The coating of small substrate surfaces that are wire bonded either before or after coating is considerably more difficult than coating a continuous strip of material.
Thus, the Kajiura et al. patent does not show or suggest an electrical energy storage device in which the individual anode or cathode plates are connected by a wire or by a narrow strip of material having opposed planar surfaces that do not extend laterally beyond edges of the anode or cathode plates. To the contrary, Kajiura et al. teach away from such a device structure.
Additionally, none of the references cited above disclose an electrical energy storage device including at least two anodes that are connected to a common terminal within the capacitor casing.